Porous membrane

ABSTRACT

A porous membrane is provided including a compound having a hydrophobic group and a nonionic hydrophilic group, an inorganic powder, and a binder resin.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a Section 371 of International Application No.PCT/JP2015/069109, filed Jul. 2, 2015, not yet published, and thedisclosure of which is incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a porous membrane.

BACKGROUND ART

Non-aqueous electrolyte secondary batteries such as a lithium ionsecondary battery are widely used as batteries for use in personalcomputers, cellular phones, portable information terminals and so on.

In a non-aqueous electrolyte secondary battery, a separator is generallyused as a member for separating a positive electrode and a negativeelectrode. Conventionally, a porous membrane formed of polyolefin havebeen used as a separator, there is a problem that heat resistance is notsatisfactory.

As a separator that is excellent in heat resistance, for example, PatentDocument 1 proposes a separator in which a porous membrane formed ofinorganic powder and polyvinyl alcohol is laminated on a porous membraneformed of polyolefin.

PRIOR ART DOCUMENTS Patent Documents

Patent Document 1: JP-A-2008-186721

SUMMARY OF THE INVENTION Problems to be Solved by the Invention

However, the separator in which a porous membrane containing inorganicpowder is laminated on a porous membrane formed of polyolefin faces theproblem that it is susceptible to curling, and the workability duringbattery assembling deteriorates.

Means for Solving the Problems

The present invention includes the following aspects.

-   [1] A porous membrane comprising a compound having a hydrophobic    group and a nonionic hydrophilic group, an inorganic powder, and a    binder resin.-   [2] The porous membrane according to [1], wherein the compound    having a hydrophobic group and a nonionic hydrophilic group is a    nonionic surfactant.-   [3] The porous membrane according to [1] or [2], wherein the    inorganic powder is a metal oxide, a meal hydroxide, or a metal    carbonate.-   [4] The porous membrane according to any one of [1] to [3], wherein    the nonionic hydrophilic group has a polyoxyethylene structure.-   [5] The porous membrane according to any one of [1] to [4], wherein    the binder resin is a water-soluble resin.-   [6] A laminated porous film comprising the porous membrane according    to any one of [1] to [5] and another porous membrane that is    different from the porous membrane according to any one of [1] to    [5], wherein these are laminated.-   [7] A coating liquid comprising a compound having a hydrophobic    group and a nonionic hydrophilic group, an inorganic powder, a    binder resin, and a solvent.-   [8] A non-aqueous electrolyte secondary battery separator comprising    the porous membrane according to any one of [1] to [5].-   [9] A non-aqueous electrolyte secondary battery comprising the    non-aqueous electrolyte secondary battery separator according to    [8].-   [10] A non-aqueous electrolyte secondary battery separator    comprising the laminated porous film according to [6].-   [11] A non-aqueous electrolyte secondary battery comprising the    non-aqueous electrolyte secondary battery separator according to    [10].

Effect of the Invention

According to the present invention, it is possible to obtain a laminatedporous film that is insusceptible to curling, in which a porous membraneformed of polyolefin, and a porous membrane containing inorganic powderare laminated.

MODE FOR CARRYING OUT THE INVENTION

<Present Porous Membrane>

The porous membrane of the present invention (hereinafter also referredto as the present porous membrane) has interconnected fine pores inside.Since the present porous membrane is porous, gas, liquid, ions and so oncan permeate from one side to the other side. Also, since the presentporous membrane contains inorganic powder, it has high heat resistanceand can impart shape stability at high temperatures to the laminatedporous film comprising the present porous membrane. Therefore, thepresent porous membrane is preferably comprised in a non-aqueouselectrolyte battery separator.

Further, by comprising a compound having a hydrophobic group and anonionic hydrophilic group (hereinafter also referred to as a presentcompound), the present porous membrane can prevent curling that occursin a laminated porous film comprising the present porous membrane.

Since the porous membrane formed of polyolefin and the porous membranecomprising an inorganic powder have different polarities, they aredifferent in affinity with water, and can be different in amount ofwater absorption when they are put under the same environment.Therefore, in the laminated porous film in which a porous membraneformed of polyolefin and a porous membrane comprising an inorganicpowder are laminated, difference arises in dimensional variation in eachmembrane, and curling occurs when the porous membrane formed ofpolyolefin and the porous membrane comprising an inorganic powder absorbwater.

Since the inorganic powder generally has high polarity, it stronglyinteracts with water. It is assumed that interaction between such aninorganic powder and a nonionic hydrophilic group possessed by thepresent compound causes adhesion of the present compound to the surfaceof the inorganic powder, and by covering the surface of the inorganicpowder with a hydrophobic group possessed by the present compound,interaction between the inorganic powder and water can be reduced.Accordingly, it is possible to reduce the moisture content of thepresent porous membrane, and curling is suppressed because the moisturecontent is approximate to that of the porous membrane formed ofpolyolefin.

The moisture content of the present porous membrane is preferably lessthan 0.15% by mass. When the moisture content of the porous membrane isless than 0.15% by mass, the curling amount tends to be further reduced,and the charge-discharge cycle characteristic of the non-aqueouselectrolyte secondary battery comprising the present porous membranetends to increase.

<Compound having Hydrophobic Group and Nonionic Hydrophilic Group>

As the nonionic hydrophilic group, groups having a polyoxyethylenestructure, and a hydroxyl group can be recited. Also, the presentcompound preferably lacks an ionic group such as an anionic group and acationic group. The anionic group used herein refers to salts such assulfonates and carboxylates, and acid groups having a pKa of less than10, e.g., sulfonic acid and carboxylic acid. That is, general hydroxylgroups having a pKa of 10 or more are not anionic groups, but correspondto nonionic groups.

Examples of the hydrophobic group include a hydrocarbon group, a groupcontaining a fluorocarbon group, and a group containing silicon, with ahydrocarbon group being preferred.

The hydrocarbon group is preferably a hydrocarbon group having 3 to 30carbon atoms. Examples of the hydrocarbon group having 3 to 30 carbonatoms include a propyl group, an isopropyl group, a butyl group, anisobutyl group, a sec-butyl group, a t-butyl group, a pentyl group, anisopentyl group, a hexyl group, an isohexyl group, a heptyl group, anisoheptyl group, an octyl group, an isooctyl group, a nonyl group, anisononyl group, a decyl group, an undecyl group, a dodecyl group, atridecyl group, a tetradecyl group, a pentadecyl group, a hexadecylgroup, a heptadecyl group, an octadecyl group, a nonadecyl group, anicosyl group (=eicosyl group), a henicosyl group (=heneicosyl group), adocosyl group, a tricosyl group, a tetracosyl group, a pentacosyl group,a hexacosyl group, a heptacosyl group, an octacosyl group, a nonacosylgroup, a triacontyl group, a propenyl group, an allyl group, anisopropenyl group, a butenyl group, an isobutenyl group, a pentenylgroup, a hexenyl group, a heptenyl group, an octenyl group, a nonenylgroup, a decenyl group, an undecenyl group, a dodecenyl group, atridecenyl group, a tetradecenyl group, a pentadecenyl group, ahexadecenyl group, a heptadecenyl group, an octadecenyl group, anonadecenyl group, an icosenyl group (=eicosenyl group), a henicosenylgroup (=heneicosenyl group), a docosenyl group, a tricosenyl group, atetracosenyl group, a pentacosenyl group, a hexacosenyl group, aheptacosenyl group, an octacosenyl group, a nonacosenyl group, atriacontenyl group, a propynyl group, a 2-propynyl group, an isopropynylgroup, a butynyl group, an isobutynyl group, a pentynyl group, a hexynylgroup, a heptynyl group, an octynyl group, a nonynyl group, a decenylgroup, an undecenyl group, a dodecenyl group, a tridecenyl group, atetradecenyl group, a pentadecenyl group, a hexadecenyl group, aheptadecenyl group, an octadecenyl group, a nonadecenyl group, anicosenyl group (=eicosenyl group), a henicosenyl group (=heneicosenylgroup), a docosenyl group, a tricosenyl group, a tetracosenyl group, apentacosenyl group, a hexacosenyl group, a heptacosenyl group, anoctacosenyl group, a nonacosenyl group, and a triacontynyl group.

The group containing a fluorocarbon group is preferably a groupcontaining a fluorocarbon group having 3 to 30 carbon atoms. As thegroup containing a fluorocarbon group having 3 to 30 carbon atoms, agroup in which part or all of the hydrogen atoms on the hydrocarbongroup have been substituted by fluorine atoms is recited and examplesthereof include a perfluoropropyl group, an isoperfluoropropyl group, aperfluorobutyl group, an isoperfluorobutyl group, a sec-perfluorobutylgroup, a t-perfluorobutyl group, a perfluoropentyl group, anisoperfluoropentyl group, a perfluorohexyl group, an isoperfluorohexylgroup, a perfluoroheptyl group, an isoperfluoroheptyl group, aperfluorooctyl group, an isoperfluorooctyl group, a perfluorononylgroup, an isoperfluorononyl group, a perfluorodecyl group, aperfluoroundecyl group, a perfluorododecyl group, a perfluorotridecylgroup, a perfluorotetradecyl group, a perfluoropentadecyl group, aperfluorohexadecyl group, a perfluoroheptadecyl group, aperfluorooctadecyl group, a perfluorononadecyl group, a perfluoroicosylgroup (=perfluoroeicosyl group), a perfluorohenicosyl group(=perfluoroheneicosyl group), a perfluorodocosyl group, aperfluorotricosyl group, a perfluorotetracosyl group, aperfluoropentacosyl group, a perfluorohexacosyl group, aperfluoroheptacosyl group, a perfluorooctacosyl group, aperfluorononacosyl group, a perfluorotriacontyl group, aperfluoropropenyl group, a perfluoroallyl group, a isoperfluoropropenylgroup, a perfluorobutenyl group, an isoperfluorobutenyl group, aperfluoropentenyl group, a perfluorohexenyl group, a perfluoroheptenylgroup, a perfluorooctenyl group, a perfluorononenyl group, aperfluorodecenyl group, a perfluoroundecenyl group, a perfluorododecenylgroup, a perfluorotridecenyl group, a perfluorotetradecenyl group, aperfluoropentadecenyl group, a perfluorohexadecenyl group, aperfluoroheptadecenyl group, a perfluorooctadecenyl group, aperfluorononadecenyl group, a perfluoroicosenyl group(=perfluoroeicosenyl group), a perfluorohenicosenyl group(=perfluoroheneicosenyl group), a perfluorodocosenyl group, aperfluorotricosenyl group, a perfluorotetracosenyl group, aperfluoropentacosenyl group, a perfluorohexacosenyl group, aperfluoroheptacosenyl group, a perfluorooctacosenyl group, aperfluorononacosenyl group, a perfluorotriacontenyl group, aperfluoropropynyl group, a 2-perfluoropropynyl group, anisoperfluoropropynyl group, a perfluorobutynyl group, anisoperfluorobutynyl group, a perfluoropentynyl group, a perfluorohexynylgroup, a perfluoroheptynyl group, a perfluorooctynyl group, aperfluorononynyl group, a perfluorodecenyl group, a perfluoroundecenylgroup, perfluorododecenyl group, a tridecenyl group, a tetradecenylgroup, a pentadecenyl group, a hexadecenyl group, a heptadecenyl group,a perfluorooctadecenyl group, a perfluorononadecenyl group, aperfluoroicosenyl group (=perfluoroeicosenyl group),perfluorohenicosenyl group (=perfluoroheneicosenyl group), aperfluorodocosenyl group, a perfluorotricosenyl group, aperfluorotetracosenyl group, a perfluoropentacosenyl group, aperfluorohexacosenyl group, a perfluoroheptacosenyl group, aperfluorooctacosenyl group, a perfluorononacosenyl group, and aperfluorotriacontanyl group.

The hydrocarbon group and the group containing a fluorocarbon group maybe coupled with an ether linkage, a thioether linkage, an ester linkage,an amide linkage, or the like.

Examples of the group containing silicon include an alkylsilyl group, adialkylsilyl group, a trialkylsilyl group, an alkyl siloxane, a dialkylsiloxane, and a trialkyl siloxane.

The present compound is preferably a nonionic surfactant.

Examples of the present compound include polyethyleneglycol-polypropylene glycol block copolymers such as polyethyleneglycol-polypropylene glycol diblock copolymer, and polypropyleneglycol-polyethylene glycol-polypropylene glycol triblock copolymer;compounds having a polyoxyethylene structure, e.g., polyoxyethylenealkyl ether, polyoxyethylene alkylphenyl ether, polyethylene glycolfatty acid ester, polyethylene oxide polypropylene oxide blockcopolymer, polyoxyethylene fatty acid amide, and ethyleneoxide-propylene oxide copolymer; and sorbitan derivatives such aspolyoxyethylene sorbitan fatty acid ester. Polyoxyethylenealkyl ethersare preferred.

Examples of the polyoxyethylene alkyl ether include polyoxyethylenemethyl ether, polyoxyethylene ethyl ether, polyoxyethylene propyl ether,polyoxyethylene isopropyl ether, polyoxyethylene butyl ether,polyoxyethylene isobutyl ether, polyoxyethylene sec-butyl ether,polyoxyethylene-t-butyl ether, polyoxyethylene pentyl ether,polyoxyethylene isopentyl ether, polyoxyethylene hexyl ether,polyoxyethylene isohexyl ether, polyoxyethylene heptyl ether,polyoxyethylene isoheptyl ether, polyoxyethylene octyl ether,polyoxyethylene isooctyl ether, polyoxyethylene nonyl ether,polyoxyethylene isononyl ether, polyoxyethylene decyl ether,polyoxyethylene undecyl ether, polyoxyethylene dodecyl ether,polyoxyethylene tridecyl ether, polyoxyethylene tetradecyl ether,polyoxyethylene pentadecyl ether, polyoxyethylene hexadecyl ether,polyoxyethylene heptadecyl ether, polyoxyethylene octadecyl ether,polyoxyethylene nonadecyl ether, polyoxyethylene icosyl ether(=polyoxyethylene eicosyl ether), polyoxyethylene henicosyl ether(=polyoxyethylene heneicosyl ether), polyoxyethylene docosyl ether,polyoxyethylene tricosyl ether, polyoxyethylene tetracosyl ether,polyoxyethylene pentacosyl ether, polyoxyethylene hexacosyl ether,polyoxyethylene heptacosyl ether, polyoxyethylene octacosyl ether,polyoxyethylene nonacosyl ether, and polyoxyethylene triacontyl ether.

The present compound is easily available on the market. Examples ofcommercially available products include “EMULGEN (registered trademark,available from Kao Corporation)”, “Newcol (available from NipponNyukazai Co., Ltd.)”, “LEOX (registered trademark, available from LionCorporation)”, “LEOCOL (registered trademark, available from LionCorporation)”, “LIONOL (registered trademark, available from LionCorporation)”, “LEOSOLB (registered trademark, available from LionCorporation)”, “LAOL (registered trademark, available from LionCorporation)”, “EMULMIN (registered trademark, available from SanyoChemical Industries, Ltd.)”, “SANNONIC (registered trademark, availablefrom Sanyo Chemical Industries, Ltd.)” “NEWPOL (registered trademark,available from Sanyo Chemical Industries, Ltd.)”, and “SANMORIN(registered trademark, available from Sanyo Chemical Industries, Ltd.)”.

The content of the present compound is preferably 0.05 to 10 parts bymass with respect to 100 parts by mass of the inorganic powder. It ispreferably 0.1 parts by mass or more, more preferably 0.2 parts by massor more, further preferably 0.3 parts by mass or more. Also, it ispreferably 5 parts by mass or less, more preferably 3 parts by mass orless, further preferably 1.5 parts by mass or less.

When the content of the present compound exceeds 10 parts by mass withrespect to 100 parts by mass of the inorganic powder, heat resistance ofthe present porous membrane tends to be impaired.

<Inorganic Powder>

Examples of the inorganic powder include metal oxides, metal hydroxides,metal carbonates, metal nitrides, metal carbides, metal hydroxides, andsulfates of metal, and metal oxides, metal hydroxides, and metalcarbonates are preferred, and metal oxides are more preferred.

The metal oxide may contain other metal components such as metalhydroxide and metal carbonate. The percentage of other metal componentcontained in the metal oxide is typically 30% by mass or less,preferably 20% by mass or less, more preferably 10% by mass or less,further preferably 5% by mass or less, particularly preferably 1% bymass or less, with respect to the total amount of metal oxide. Amongmetal oxides, alumina is preferred from the viewpoint of furtherimproving the chemical stability, and the shape stability at hightemperatures, and among these α-alumina is more preferred.

Concrete examples of the inorganic powder include calcium oxide,magnesium oxide, titanium oxide, alumina, aluminum hydroxide, magnesiumhydroxide, calcium carbonate, magnesium carbonate, barium carbonate,calcium sulfate, magnesium sulfate, barium sulfate, talc, clay, kaolin,silica, hydrotalcite, diatom earth, mica, zeolite, and glass. These maybe used singly or in combination of two or more kinds.

The percentage of the inorganic powder in the present porous membranetypically exceeds 50% by mass of the present porous membrane, and it ispreferably 70% by mass or more, more preferably 90% by mass or more,further preferably 95% by mass or more. Also, it is preferably 99.5% bymass or less, more preferably 99% by mass or less, and furtherpreferably 98% by mass or less.

<Binder Resin>

The binder resin binds inorganic powder, and also has the function ofbinding the present porous membrane, and a porous membrane other thanthe present porous membrane (hereinafter, also referred to as otherporous membrane). The binder resin is preferably a resin that isinsoluble to an electrolyte solution of a non-aqueous electrolytesecondary battery, and is electrochemically stable within the use rangeof the non-aqueous electrolyte secondary battery. Examples of the binderresin include polyolefins such as polyethylene and polypropylene;fluorine-containing resins such as poly(vinylidene fluoride) andpolytetrafluoroethylene; fluorine-containing rubbers such as vinylidenefluoride-hexafluoropropylene-tetrafluoroethylene copolymer andethylene-tetrafluoroethylene copolymer; styrene-butadiene copolymer andhydride thereof; (meth)acrylate ester copolymers such as methacrylateester copolymer, acrylonitrile-acrylate ester copolymer, andstyrene-acrylate ester copolymer; rubbers such as ethylene-propylenerubber; polyvinyl acetate; resins having a melting point or a glasstransition temperature of 180° C. or higher such as polyphenylene ether,polysulfone, polyether sulfone, poly phenylene sulfide, polyether-imide,polyamide, polyimide, polyamide-imide, polyether amide, polyester,aromatic polyester, and polyetherether ketone; polycarbonate;polyacetal; and copolymers of water-soluble resins such as carboxyalkylcellulose, alkyl cellulose, hydroxyalkyl cellulose, starch, polyvinylalcohol, sodium alginate, polyethylene glycol, cellulose ether,polyacrylic acid, polyacrylamide, and polymethacrylic acid. Among these,fluorine-containing resins, fluorine-containing rubbers, resins having amelting point or a glass transition temperature of 180° C. or higher andwater-soluble resins are preferred. Fluorine-containing resins,fluorine-containing rubbers, resins having a melting point or a glasstransition temperature of 180° C. or higher are preferred because theyare highly stable in the use range of the nonaqueous electrolytebattery. Water-soluble resins are preferred in terms of the process andthe environmental load. Among the water-soluble resins, carboxyalkylcellulose, alkyl cellulose, hydroxyalkyl cellulose, starch, polyvinylalcohol, and sodium alginate are preferred, and cellulose ether is morepreferred. These binder resins maybe used singly or in combination oftwo or more kinds.

Examples of cellulose ether include carboxymethyl cellulose (CMC),hydroxyethyl cellulose (HEC), carboxyethyl cellulose, methyl cellulose,ethyl cellulose, cyanethyl cellulose, and oxyethyl cellulose. Amongthese, CMC and HEC that are excellent in chemical and thermal stabilityare preferred, and CMC is more preferred.

Polyamide is preferably aromatic polyamide, particularly preferablypara-directing aromatic polyamide (hereinafter, also referred to as“para-aramid”).

Para-aramid is typically obtained by condensation polymerization ofpara-directing aromatic diamine and para-directing aromatic dicarboxylichalide, and is substantially composed of a repeating unit whose amidebond is bound at a para position or the like orientation position of thearomatic ring (for example, orientation position extending coaxially orparallel in the opposite direction such as 4,4′-biphenylene,1,5-naphthalene, and 2,6-naphthalene). Examples of para-aramid includepara-directing para-aramids and para-aramids having a structurecorresponding to a para-directing para-aramid such as poly(paraphenyleneterephthalamide), poly(para-benzamide),poly(4,4′-benzanilideterephthalamide),poly(paraphenylene-4,4′-biphenylenedicarboxylic amide),poly(paraphenylene-2,6-naphthalenedicarboxylic amide),poly(2-chloro-paraphenylene terephthalamide), and paraphenyleneterephthalamide/2,6-dichloroparaphenylene terephthalamide copolymer.

Polyimide is preferably aromatic polyimide, more preferably whollyaromatic polyimide. Aromatic polyimide is typically produced bycondensation polymerization of a dianhydride of an aromatic compound anda diamine. Examples of the dianhydride include pyromellitic dianhydride,3,3′,4,4′-diphenyl sulfone tetracarboxylic dianhydride, 3,3′,4,4′-benzphenone tetracarboxylic dianhydride,2,2′-bis(3,4-dicarboxyphenyl)hexafluoropropane, and 3,3′,4,4′-biphenyltetracarboxylic dianhydride. Examples of the diamine includeoxydianiline, paraphenylene diamine, benzphenonediamine, 3,3′-methylenedianiline, 3,3′-diaminobenzphenone, 3,3′-diaminodiphenylsulfone, and1,5′-naphthalenediamine.

Polyamideimide is preferably aromatic polyamideimide. Aromaticpolyamideimide is typically obtainable by condensation polymerization ofan aromatic dicarboxylic acid and an aromatic diisocyanate, or may beobtained by condensation polymerization of an aromatic dianhydride andan aromatic diisocyanate. Examples of the aromatic dicarboxylic acidinclude isophthalic acid and terephthalic acid. Examples of the aromaticdianhydride include trimellitic anhydride. Examples of the aromaticdiisocyanate include 4,4′-diphenylmethane diisocyanate, 2,4-tolylenediisocyanate, 2,6-tolylene diisocyanate, ortho-tolylane diisocyanate,and m-xylene diisocyanate.

The percentage of the inorganic powder in the total amount of the binderresin and the inorganic powder in the present porous membrane typicallyexceeds 50% by mass, preferably 70% by mass or more, more preferably 90%by mass or more, further preferably 95% by mass or more. Also it ispreferably 99.5% by mass or less, more preferably 99% by mass or less,further preferably 98% by mass or less. When the percentage of theinorganic powder falls within the range specified above, the presentporous membrane with excellent balance between ion permeability andunlikeliness of powder dropping is obtained. Powder dropping is aphenomenon that the inorganic powder peels off from the present porousmembrane.

The present porous membrane may contain other ingredient as long asfunctions of the present porous membrane are not impaired. Examples ofthe other ingredient include a dispersing agent, a plasticizer, and a pHmodifier.

The thickness of the present porous membrane is typically 0.1 to 20 μm,preferably 1 to 10 μm. When the thickness is less than 0.1 μm, heatresistance of the non-aqueous electrolyte secondary battery separatorincluding the present porous membrane tends to be insufficient. Forexample, in the case of using a laminated porous film in which thepresent porous membrane and a porous membrane formed of polyolefin arelaminated, as a non-aqueous electrolyte secondary battery separator, theseparator can contract when the thickness of the present porous membraneis less than 0.1 μm because the separator cannot bear the thermalcontraction of the porous membrane formed of polyolefin when heatgeneration occurs in the non-aqueous electrolyte secondary battery dueto an accident or the like. On the other hand, when the thicknessexceeds 20 μm, the thickness of the separator is large, and the capacityof the battery may be reduced.

The porosity of the present porous membrane is typically 20 to 80% byvolume, preferably 30 to 70% by volume.

When the porosity is less than 20% by volume, the retaining amount ofthe electrolyte solution can decrease, whereas when the porosity is morethan 80% by volume, the heat resistance of the present porous membranemay be impaired. In other words, there is a fear that the current cannotbe blocked when the battery severely generates heat.

The pore diameter of pores possessed by the present porous membrane ispreferably 3 μm or less, more preferably 1 μm or less from the viewpoint of having excellent ion permeability and preventing entry ofparticles into the positive electrode or the negative electrode.

The permeability of the present porous membrane is typically representedby air permeability. Air permeability of the present porous membrane istypically 30 to 1000 sec/100 cc, preferably 50 to 800 sec/100 cc.

A mass per unit area of the present porous membrane is typically 4 to 20g/m², preferably 5 to 12 g/m². When the mass per unit area is less than4 g/m², the strength can be insufficient, whereas when it is more than20 g/m², the thickness of the present porous membrane increases, and thecapacity of the battery may be reduced.

<Laminated Porous Film>

The present porous membrane is used in the form of a laminated porousfilm in which it is laminated with another porous membrane (hereinafteralso referred to as the present laminated porous film), as a non-aqueouselectrolyte secondary battery separator. Examples of another porousmembrane include paper of viscose rayon, natural cellulose or the like;mixed paper obtained by papering fibers such as cellulose, polyester orthe like; electrolytic paper; kraft paper; Manila paper; polyethylenenonwoven fabric, polypropylene nonwoven fabric, polyester nonwovenfabric, glass fiber, porous polyolefin (e.g., porous polyethylene,porous polypropylene), porous polyester, aramid fiber, polybutyleneterephthalate nonwoven fabric, para-wholly aromatic polyamide,poly(vinylidene fluoride), tetrafluoroethylene, copolymer of vinylidenefluoride and propylene hexafluoride, nonwoven fabric or porous membraneof fluorine-containing resin such as fluorine rubber or the like; andproton conductive polymer. A porous membrane formed of polyolefin(hereinafter, also referred to as polyolefin membrane) is preferred.

The present laminated porous film may have another porous membrane and aplurality of the present porous membranes, and for example, the presentporous membranes may be laminated on both sides of another porousmembrane. When the present porous membranes are laminated on both sidesof another porous membrane, the present porous membranes may containdifferent present compounds, an inorganic powder and binder resins.

The polyolefin membrane imparts a function of shutdown to the presentlaminated porous film by melting to lose the pores when the batteryseverely generates heat. Further, since the present porous membrane hasheat resistance at high temperatures where shutdown occurs, the presentlaminated porous film has shape stability even at high temperatures.

The moisture content of the present laminated porous membrane ispreferably less than 0.15% by mass.

When the moisture content of the porous membrane is 0.15% by mass ormore, the charge-discharge cycle characteristic of the battery may beimpaired.

The 50% breakdown voltage of the non-aqueous electrolyte secondarybattery that includes the present laminated porous film as a non-aqueouselectrolyte secondary battery separator is preferably 4.40 V or more.The non-aqueous electrolyte secondary battery has a battery voltage ofas large as 4.40 V, and even when the battery capacity is large,abnormal heat generation is suppressed at the time of occurrence ofinternal short-circuit, or in other words, it has excellent safety forinternal short-circuit.

The membrane resistance of the laminated porous film is preferably 0.25to 5.00 Ω·cm² from the view point of battery characteristics (ionpermeability, load characteristic). When the membrane resistance is lessthan 0.25 Ω·cm², ion permeability is excellent; however, the risk ofoccurrence of micro short circuit can increase. When the membraneresistance exceeds 5.00 Ω·cm², excellent ion permeability is notobtained, and battery characteristics may be impaired. For increasingthe membrane resistance, for example, the thickness of the polyolefinmembrane and/or the present porous membrane can be increased, or theporosity thereof can be reduced. For reducing the membrane resistance,the thickness of the polyolefin membrane and/or the present porousmembrane can be reduced, or the porosity thereof can be increased.

Thickness of the present laminated porous film is typically 5 to 75 μm,preferably 10 to 50 μm. When the thickness of the laminated porous filmis less than 5 μm, the laminated porous film can be easily broken,whereas when it exceeds 75 μm, thickness of the present laminated porousfilm increases, and the capacity of the battery may be reduced.

The volume per unit area of the present porous membrane contained in thepresent laminated porous film is typically 0.5 to 20 cc/m², preferably 1to 10 cc/m² from the view points of stability at the time of heating andbattery characteristics. When the volume per unit area is less than 0.5cc/m², the present laminated porous film can be easily broken underheating, whereas when it exceeds 20 cc/m², the thickness of the presentlaminated porous film increases and the capacity of the battery can bereduced. When the present porous membranes are laminated on both sidesof another porous membrane, the volume per unit area is the total valueof both sides.

Air permeability of the present laminated porous film is typically 50 to2000 sec/100 cc, preferably 70 to 1000 sec/100 cc. When the airpermeability exceeds 2000 sec/100 cc, the battery characteristics (ionpermeability, load characteristic) may be impaired.

The present laminated porous film may contain porous layers such as anadhesive layer, a protective layer and so on other than another porousmembrane and the present porous membrane as long as the object of thepresent invention is not impaired.

<Polyolefin Membrane>

Examples of the polyolefin contained in the polyolefin membrane includehigh molecular weight homopolymers or copolymers obtained bypolymerizing ethylene, propylene, 1-butene, 4-methyl-1-pentene, 1-hexeneor the like. High molecular weight polyethylene is preferred. Thesepolyolefins may be used singly or in combination of two or more kinds.

The molecular weight of the polyolefin is preferably 1 ×10⁵ to 15×10⁶ byweight average molecular weight from the view point of preventingsolution of the polyolefin membrane into the electrolyte solution whenthe present laminated porous film is used in a non-aqueous electrolytesecondary battery, as a non-aqueous electrolyte secondary batteryseparator.

The percentage of the polyolefin contained in the polyolefin membranetypically exceeds 50% by volume, preferably 70% by volume or more, morepreferably 90% by volume or more, further preferably 95% by volume ormore of the entire solids contained in the polyolefin membrane.

The polyolefin membrane may contain other ingredient than polyolefin aslong as the function of the polyolefin membrane is not impaired.

The thickness of the polyolefin membrane is typically 4 to 50 μm,preferably 5 to 30 μm. When the thickness is less than 4 μm, thestrength of the present laminated porous film can be insufficient,whereas when it is more than 50 μm, the thickness of the presentlaminated porous film increases, and the capacity of the battery can bereduced.

Porosity of the polyolefin membrane is typically 20 to 80% by volume,preferably 30 to 70% by volume.

When the porosity is less than 20% by volume, the retaining amount ofthe electrolyte solution can decrease, whereas when the porosity is morethan 80% by volume, lost of pores at high temperatures where shutdownoccurs can be insufficient, or in other words, there is a fear that thecurrent cannot be blocked when the battery severely generates heat.

The pore diameter of pores possessed by the polyolefin membrane ispreferably 3 μm or less, more preferably 1 μm or less from the viewpoint of having excellent ion permeability and preventing entry ofparticles into the positive electrode or the negative electrode when thepresent laminated porous film is used as a non-aqueous electrolytesecondary battery separator.

The polyolefin membrane has interconnected pores inside, and allowspermeation of gas, liquid, ions and so on from one side to the otherside. The permeability is typically represented by air permeability. Airpermeability of the polyolefin membrane is typically 30 to 1000 sec/100cc, preferably 50 to 800 sec/100 cc.

The mass per unit area of the polyolefin membrane is typically 4 to 15g/m², preferably 5 to 12 g/m². When the mass per unit area is less than4 g/m², the strength of the present laminated porous film can beinsufficient, whereas when it is more than 15 g/m², the thickness of thepresent laminated porous film increases, and the capacity of the batterycan be reduced.

<Method for Producing Present Porous Membrane>

As a method for producing the present porous membrane, a method ofapplying a coating liquid containing the present compound, an inorganicpowder, and a binder resin (hereinafter also referred to as the presentcoating liquid) to a base material to form the present porous membrane,and removing the base material to complete the membrane, and a method ofapplying the present coating liquid on a base material, dipping it in asolvent that mingles with the coating liquid but is not soluble in thebinder resin, followed by drying to form a porous membrane, andthereafter removing the base material can be recited.

The present coating liquid typically contains a solvent that dissolves abinder resin. The present coating liquid may contain a pH modifier, adispersing agent, a plasticizer, alcohol and the like as long as theobject of the present invention is not impaired, and preferably containsalcohol.

Examples of the alcohol include methanol, ethanol, 1-propanol, isopropylalcohol, 2-butanol, tert-butyl alcohol, 1-butanol, isobutyl alcohol,sec-butyl alcohol, t-butyl alcohol, pentyl alcohol, isopentyl alcohol,hexyl alcohol, isohexyl alcohol, heptyl alcohol, isoheptyl alcohol,octyl alcohol, isooctyl alcohol, octyl alcohol, isooctyl alcohol, nonylalcohol, isononyl alcohol, decyl alcohol, ethylene glycol, propyleneglycol, and butanediol.

The content of the alcohol in the present coating liquid is notparticularly limited, and may be such an amount that the property offacilitating application to other porous membrane can be obtained. Thecontent of the alcohol in the present coating liquid is preferably 1 to1000 parts by mass, more preferably 2 to 500 parts by mass, furtherpreferably 3 to 300 parts by mass, still more preferably 5 to 200 partsby mass based on 1 part by mass of the binder resin.

<Method for Producing Another Porous Membrane>

Another porous membrane may be produced by a known method or acommercially available product may be used.

<Method for Producing Polyolefin Membrane>

As the polyolefin membrane, those produced by forming fine holes bymonoaxially or biaxially stretching a film or sheet formed of polyolefincan be used. As a method for producing the polyolefin membrane, forexample, a method including forming a film by adding a plasticizer tothermoplastic resin and removing the plasticizer with an appropriatesolvent as described in JP-A-7-29563 can be recited. For example, whenthe polyolefin membrane is formed of a polyolefin resin containing ahigh molecular weight polyethylene having a weight average molecularweight of more than 1000000, and a low molecular weight polyolefinhaving a weight average molecular weight of 10000 or less, it ispreferably produced by the method including the following steps from theview point of the production cost.

-   (a) Kneading 100 parts by mass of a high molecular weight    polyethylene, 5 to 200 parts by mass of a low molecular weight    polyolefin, and 100 to 400 parts by mass of an inorganic filler such    as calcium carbonate to obtain a polyolefin resin composition.-   (b) Forming a sheet by using the polyolefin resin composition.-   (c) Removing the inorganic filler from the sheet obtained in step    (b).-   (d) Stretching the sheet obtained in step (c) to obtain a polyolefin    membrane.    <Method for Producing Present Laminated Porous Film>

As a method for laminating the present porous membrane and anotherporous membrane, a method of separately producing another porousmembrane and the present porous membrane and then laminating them, and amethod of applying the present coating liquid to another porous membraneto form the present porous membrane can be recited, and the lattermethod is preferred for its simplicity.

As the method of applying the present coating liquid to another porousmembrane to form the present porous membrane, for example, the methodincluding the following steps can be recited.

-   (a) Preparing a coating liquid in which inorganic powder is    dispersed in a solution of the present compound and the binder resin    dissolved in a solvent,-   (b) Applying the coating liquid to another porous membrane to form a    coating membrane,-   (c) Depositing the binder resin from the coating membrane by solvent    removal or dipping in a solvent that does not dissolve the binder    resin, and drying as needed.

When the binder resin is an aromatic polyamide, as the solvent thatdissolves the binder resin, polar amide solvents and polar urea solventscan be recited. Concrete examples include N,N-dimethylformamide,N,N-dimethylacetamide, N-methyl-2-pyrrolidone (NMP), and tetramethylurea.

When the binder resin is a para-aramid, it is preferred to add achloride of alkali metal or alkali earth metal for the purpose ofimproving the solubility of the para-aramid in the solvent. Concreteexamples include lithium chloride and calcium chloride. The addingamount of the chloride is preferably in the range of 0.5 to 6.0 mol,more preferably in the range of 1.0 to 4.0 mol per 1.0 mol of amidegroups in the para-amide. When the chloride is less than 0.5 mol, thesolubility of the para-aramid can be insufficient, whereas the chlorideexceeding 6.0 mol can be undesired because the solubility of thechloride into the solvent is exceeded. The percentage of the chloride inthe total amount of the coating liquid is preferably in the range of 2to 10% by mass. Generally, when the chloride of alkali metal or alkaliearth metal is less than 2% by mass, the solubility of the para-aramidcan be insufficient, and when it exceeds 10% by mass, the solubility ofthe chloride can be insufficient.

As the solvent that dissolves the binder resin when the binder resin isan aromatic polyimide, dimethyl sulfoxide, cresol, o-chlorophenol andthe like, besides those exemplified as a solvent that dissolves anaromatic polyamide can be preferably used.

As the solvent that dissolves the binder resin when the binder resin isa water-soluble resin, water, alcohols such as methanol, ethanol andisopropanol, acetone, toluene, xylene, hexane, N-methylpyrrolidone, N,N-dimethylacetamide, and N,N-dimethylformamide can be used singly, or aplurality of these solvents can be mixed as far as they are compatible.Among these, from the view point of process and environmental loads,preferably, water occupies 80% by mass or more of the medium, and onlywater is more preferred.

When the solvent contains water, it is preferred that another porousmembrane is subjected to a hydrophilization treatment before the solventis applied on another porous member. By subjecting another porousmembrane to the hydrophilization treatment, the coating properties arefurther improved, and a more uniform present porous membrane can beobtained. This hydrophilization treatment is effective particularly whenthe concentration of water in the solvent is high.

The hydrophilization treatment of another porous membrane may beconducted in any method, and concrete examples of the method include atreatment with a chemical such as acid or alkali, a corona treatment,and a plasma treatment.

Here, the corona treatment is advantageous in that the other porousmembrane can be hydrophilized in a relatively short time, and reformingby corona discharge is limited to the surface and the vicinity of theother porous membrane, so that high coating properties can be ensuredwithout causing change in the properties of the interior of the otherporous membrane.

Removal of the solvent from the coating liquid applied on the otherporous membrane is generally conducted by a method by drying. Also, thecoating film before drying may be dipped in a solvent that does notdissolve the binding resin, to deposit the binder resin, and then thesolvent may be removed by drying. When the coating liquid is applied onthe other porous membrane, the drying temperature of the solvent ispreferably such a temperature that does not change the air permeabilityof the other porous membrane after drying.

The method for applying the present coating liquid on another porousmembrane is not particularly limited as far as uniform wet coating ispossible, and a conventionally known method can be employed. Forexample, a capillary coating method, a spin coating method, a slit dyecoating method, a spray coating method, a roll coating method, a screenprinting method, a flexo printing method, a bar coater method, a gravurecoater method, and a dye coater method can be employed. The thickness ofthe present porous membrane to be formed can be controlled by adjustingthe applying amount of the present coating liquid, the concentration ofthe present coating liquid, and the content ratio between the inorganicpowder and the binder resin. During the coating, a resin film, a metalbelt, or a dram can be used as a support.

As the method for preparing the present coating liquid, a method ofstirring by a mechanical stirring method, an ultrasonic dispersingmethod, a high pressure dispersing method, or a media dispersing methodcan be recited. The high pressure dispersing method is more preferredbecause it can disperse the inorganic powder more uniformly.

<Non-Aqueous Electrolyte Secondary Battery>

The non-aqueous electrolyte secondary battery includes a positiveelectrode, a negative electrode, a separator for a non-aqueouselectrolyte secondary battery sandwiched between the opposing faces ofthe positive electrode and the negative electrode, and a non-aqueouselectrolyte solution.

As the non-aqueous electrolyte solution, for example, a non-aqueouselectrolyte solution prepared by dissolving a lithium salt in an organicsolvent can be used. The lithium salt can be one or a mixture of two ormore of LiClO₄, LiPF₆, LiAsF₆, LiSbF₆, LiBF₄, LiCF₃SO₃, LiN (SO₂CF₃)₂,LiC(SO₂CF₃)₃, Li₂B₁₀Cl₁₀, lower aliphatic carboxylic acid lithium salt,LiAlCl₄ and so on. Among these, those containing at least one selectedfrom the group consisting of fluorine-containing LiPF₆, LiAsF₆, LiSbF₆,LiBF₄, LiCF₃SO₃, LiN(CF₃SO₂)₂, and LiC(CF₃SO₂)₃ are preferably used.

Examples of the non-aqueous electrolyte solution include carbonates suchas propylene carbonate, ethylene carbonate, dimethyl carbonate, diethylcarbonate, ethylmethyl carbonate, 4-trifluoromethyl-1,3-dioxolan-2-one,and 1,2-di(methoxycarbonyloxy)ethane; ethers such as1,2-dimethoxyethane, 1,3-dimethoxypropane, pentafluoropropylmethylether, 2,2,3,3-tetrafluoropropyldifluoromethyl ether, tetrahydrofuran,and 2-methyltetrahydrofuran; esters such as methyl formate, methylacetate, and Y-butyrolactone; nitriles such as acetonitrile andbutyronitrile; amides such as N, N-dimethylformamide, andN,N-dimethyacetamide; carbamates such as 3-methyl-2-oxazolidon;sulfur-containing compounds such as sulfolane, dimethylsulfoxide, and1,3-propansultone or the foregoing substances into which a fluorinegroup is introduced, and typically a mixture of two or more kinds isused.

Among these, those containing carbonates are preferred, and mixtures ofcyclic carbonate and non-cyclic carbonate, or mixtures of cycliccarbonate and ethers are more preferred. As the mixtures of cycliccarbonate and non-cyclic carbonate, mixtures containing ethylenecarbonate, dimethyl carbonate and ethylmethyl carbonate are preferred inthe points that they operate in a wide temperature range, and arerefractory even when graphite materials such as natural graphite,artificial graphite and the like are used as an active material of thenegative electrode.

As the positive electrode, a collector carrying a mixture of apositive-electrode active material, a conductive agent and a binder isused. A concrete example of the positive-electrode active material thatcan be used contains a material capable of being doped or undoped withlithium ions, contains a carbonaceous material as the conductive agent,and contains a thermoplastic resin as the binder. As the materialcapable of being doped or undoped with lithium ions, a lithium compositeoxide containing at least one transition metal such as V, Mn, Fe, Co,and Ni can be recited. Among these, a lithium composite oxide having anα-NaFeO₂ structure such as lithium nickel oxide and lithium cobaltoxide, a lithium composite oxide having a spinel structure such aslithium manganese spinel are recited in the point that the averagedischarge potential is high.

The lithium composite oxide may contain various metal elements, and itis preferred to use a composite lithium nickel oxide containing at leastone metal element in such an amount that the metal element is 0.1 to 20mol %, based on the sum of the mol number of at least one metal elementselected from the group consisting of Ti, V, Cr, Mn, Fe, Co, Cu, Ag, Mg,Al, Ga, In and Sn, and the mol number of Ni in the lithium nickel oxide,because cycle performance in use with high capacity is improved.

Examples of the binder include polyvinylidene fluoride, copolymer ofvinylidene fluoride, polytetrafluoroethylene,tetrafluoroethylene-hexafluoropropylene copolymer,tetrafluoroethylene-perfluoroalkylvinyl ether copolymer,ethylene-tetrafluoroethylene copolymer, vinylidenefluoride-hexafluoropropylene-tetrafluoroethylene copolymer, andthermoplastic resins such as thermoplastic polyimide, polyethylene, andpolypropylene.

As the conductive agent, carbonaceous materials such as naturalgraphite, artificial graphite, cokes, and carbon black can be recited.As the conductive agent, these may be solely used, or for example, amixture of artificial graphite and carbon black may be used.

As the negative electrode, for example, materials capable of being dopedor undoped with lithium ions, lithium metal, lithium alloy and so on canbe used. Examples of the materials capable of being doped or undopedwith lithium ions include carbonaceous materials such as naturalgraphite, artificial graphite, cokes, carbon black, pyrocarbons, carbonfiber, a sintered organic polymer compound, and chalcogen compounds ofoxides, sulfides and the like doped or undoped with lithium ions at apotential lower than the positive electrode. As the carbonaceousmaterial, carbonaceous materials based on graphite materials such asnatural graphite and artificial graphite are referred in the point thatthey have high potential flatness, and low average discharge potential,and thus large energy density is obtained when combined with thepositive electrode.

As the negative electrode collector, Cu, Ni, stainless or the like canbe used, and Cu is preferred because it is unlikely to form an alloywith lithium, and can be easily worked into a thin film, particularly inthe lithium secondary battery. As a method for making the negativeelectrode collector carry a mixture containing a negative electrodeactive material, a pressure forming method, or a method of preparing apaste by using a solvent or the like, and applying the paste on thecollector, followed by drying and pressing to make them compressionbonded can be recited.

The shape of the battery of the present invention is not particularlylimited, and may be any of a paper shape, a coin shape, a cylindricalshape, a rectangular shape or a laminate shape.

EXAMPLES

In the following Examples, Comparative Examples, and Reference Examples,physical properties of a laminated porous film were measured accordingto the following methods.

(1) Measurement of Curling: A laminated porous film was cut into asquare shape of 8 cm×8 cm, and after retention for a day under roomtemperature and a dew point −30° C., and a rising height in an end partwas measured.

Also appearance was evaluated according to the following criteria. Cindicates a completely curled state, and the states of A and B arepreferred, and A is more preferred.

-   A: No rise in an end part.-   B: Only an end part rises, but most of the part other than the end    part does not rise, and keeps a flat state.-   C: Both end parts come close to each other, and are curling in a    cylindrical shape.    (2) Dimension Retention Rate: A laminated porous film was cut into a    square shape of 5 cm×5 cm, and a marking line of a square shape of 4    cm square was described in the center, and the film was sandwiched    between two sheets of paper, and retained at 150° C. in an oven for    1 hour, then the film was removed and the dimension of the square    shape was measured, and dimension retention rate was calculated. The    calculating method of dimension retention rate is as follows.-   Length of marking line in the vertical direction (TD) before    heating: W1-   Length of marking line in the vertical direction (TD) after heating:    W2-   Dimension retention rate (%) in the vertical direction    (TD)=W2/W1×100    (3) Air Permeability:

Measured according to JIS P8117.

Example 1

To a mixture of 100 parts by mass of alumina microparticles (trade name“AKP3000”, available from Sumitomo Chemical Co., Ltd.), 3 parts by massof carboxymethyl cellulose (Item number 1110, available from DAICELFINECHEM LTD.), and 0.5 parts by mass of polyoxyethylene alkyl ether(available from Sanyo Chemical Industries, Ltd.; Sanmorin (registeredtrademark) 11), water was added so that the solid content was 29% bymass, and the obtained mixture was stirred and mixed twice in thecondition of 2000 rpm, 30 seconds under room temperature by using aplanetary centrifugal mixer “Awatori Rentaro” (registered trade name:available from Thinky Corporation). To the obtained mixture, 14 parts bymass of isopropyl alcohol was added, to obtain a coating liquid as anuniform slurry having a solid content of 28% by weight. The obtainedcoating liquid was applied on a porous membrane of polyethylene havingsubjected to a corona treatment 20 W/(m²/min.) (thickness 12 μm,porosity 41%) by a doctor blade method, and the laminate which was theobtained coated matter was dried at 65° C. for 5 minutes to obtain alaminated porous film (1) in which the present porous membrane and theporous membrane formed of polyethylene are laminated. The mass per unitarea of the present porous membrane in the laminated porous film (1) was6.2 g/m². Physical properties of the laminated porous film (1) are shownin Table 1.

Example 2

A laminated porous film (2) was obtained in the same manner as inExample 1 except that the amount of polyoxyethylene alkyl ether of 0.5parts by mass in Example 1 was varied to 1 part by mass. The mass perunit area of the present porous membrane in the laminated porous film(2) was 6.6 g/m². Physical properties of the laminated porous film (2)are shown in Table 1.

Comparative Example 1

A laminated porous film (3) was obtained in the same manner as inExample 1 except that 0.5 parts by mass of polyoxyethylene alkyl etherin Example 1 was not added. The mass per unit area of the present porousmembrane in the laminated porous film (3) was 6.9 g/m². Physicalproperties of the laminated porous film (3) are shown in Table 1.

TABLE 1 Dimension Curling measurement retention Air Height of end ratepermeability part (cm) Appearance (%) (sec/100 cc) Example 1 0.5 B 100244 Example 2 0 A  98 254 Comparative 1.5 C 100 233 Example 1

The laminated porous films (1) and (2) obtained in Examples 1 and 2could reduce the curling amount while keeping high dimension retentionrate and air permeability.

INDUSTRIAL APPLICABILITY

According to the present invention, it is possible to obtain ahard-to-curl laminated porous film in which a porous membrane formed ofpolyolefin and a porous membrane containing inorganic powder arelaminated.

The invention claimed is:
 1. A non-aqueous electrolyte secondary batteryseparator comprising a laminated porous film comprising a first and asecond porous membrane that are different from each other, wherein thefirst and the second porous membranes are laminated, and wherein thefirst porous membrane comprises a compound having a hydrophobic groupand a nonionic hydrophilic group, an inorganic powder, and a binderresin, wherein a content of the inorganic powder is at least 50% by massand 99% by mass or less based on 100% by mass of the first porousmembrane, wherein the first porous membrane has a mass per unit area of4 g/m² to 20 g/m², wherein the laminated porous film has a moisturecontent of less than 0.15% by mass and a membrane resistance of 0.25Ω⋅cm² to 5.00 Ω⋅cm², and wherein the laminated porous film has athickness of 5 μm to 75 μm and a volume per unit area of 0.5 cc/m² to 20cc/m².
 2. A non-aqueous electrolyte secondary battery comprising thenon-aqueous electrolyte secondary battery separator according toclaim
 1. 3. The non-aqueous electrolyte secondary battery separatoraccording to claim 1, wherein the compound having a hydrophobic groupand a nonionic hydrophilic group is a nonionic surfactant.
 4. Thenon-aqueous electrolyte secondary battery separator according to claim1, wherein the inorganic powder is a metal oxide, a metal hydroxide, ora metal carbonate.
 5. The non-aqueous electrolyte secondary batteryseparator according to claim 1, wherein the nonionic hydrophilic grouphas a polyoxyethylene structure.
 6. The non-aqueous electrolytesecondary battery separator according to claim 1, wherein the binderresin is a water-soluble resin.
 7. The non-aqueous electrolyte secondarybattery separator according to claim 6, wherein the binder is acellulose ether.
 8. The non-aqueous electrolyte secondary batteryseparator according to claim 1, wherein the hydrophobic group is ahydrocarbon group.
 9. The non-aqueous electrolyte secondary batteryseparator according to claim 1, wherein the first porous membrane has amoisture content of less than 0.15% by mass.
 10. The non-aqueouselectrolyte secondary battery separator according to claim 1, wherein acontent of the compound having a hydrophobic group and a nonionichydrophilic group in the first porous membrane is 0.05 to 10 parts bymass with respect to 100 parts by mass of the inorganic powder.
 11. Thenon-aqueous electrolyte secondary battery separator according to claim1, wherein the second porous membrane comprises a polyolefin.
 12. Thenon-aqueous electrolyte secondary battery separator according to claim1, wherein a thickness of the first porous membrane is 0.1 μm to 20 μm.13. The non-aqueous electrolyte secondary battery separator according toclaim 1, wherein the first porous membrane has a porosity of 20% byvolume to 80% by volume.
 14. The non-aqueous electrolyte secondarybattery separator according to claim 1, wherein the first porousmembrane has an air permeability of 30 sec/100 cc to 1000 sec/100 cc.15. The non-aqueous electrolyte secondary battery separator according toclaim 1, wherein the laminated porous film has an air permeability of 50sec/100 cc to 2000 sec/100 cc.